Embodiments relate to a nonvolatile memory device and a method of operating the same.
In recent years, there is an increasing demand for nonvolatile memory devices which can be electrically programmed and erased and which do not require the refresh function of rewriting data at specific intervals.
The nonvolatile memory device is configured to enable electrical program and erase operations and perform the program and erase operations through the threshold voltage of a cell which varies when electrons are moved by a strong electric field applied to a thin oxide layer. During the programming operation of the nonvolatile memory device, a verification operation for determining whether a cell to be programmed has been programmed to exceed a reference voltage is performed. In the single level cell (SLC) program method, the verification voltage is only one, whereas in the multi-level cell (MLC) program method, the verification voltage is plural because cells of several states exist in a single page. For example, in the case where the most significant bit (MSB) program operation is performed in a 2-bit MLC program method, a verification operation is performed based on three verification voltages.
According to the incremental step pulse program (ISPP) method, after a pulse is applied once, three verification operations need to be performed. There is known a blind verification method of performing only some of verification operations (not all the verification operations) with the program speed taken into consideration. If the number of program/erase cycles of a nonvolatile memory device increases, there is a tendency that the program speed increases. Accordingly, there is a need for a program method with consideration taken of such a tendency.